Alain Pareilleux

Influence of nitrogen and iron limitations on lipid production by Cryptococcus curvatus grown in batch and fed-batch culture

Abstract Cryptococcus curvatus , an oleaginous yeast, was grown under iron (Fe) and nitrogen (N)-limited conditions to produce lipid with a high stearic acid (C18:0) content in batch and fed-batch culture. In batch culture, lack of ferrous ions had no evident effect on growth, lipid production or lipid composition. The highest stearic acid content in the total lipid was 14% in N-limited medium in batch culture. The combined effect of Fe and N-limitation in fed-batch culture was to increase the stearic acid content to 19% of the total lipids and the consumed carbon to nitrogen (C:N) ratio to 20 g/g. The highest biomass concentration achieved was 70 g/litre and 53% (w/w) lipid accumulated when grown for about 172 h in fed-batch culture. A C:N ratio between 20 and 50 was optimal for intracellular lipid accumulation and a ratio > 50 g/g became crucial for both growth and lipid production in fed-batch culture. The maximal C:N ratio achieved at the end of the culture was 75 g/g. Lipid yield from glucose (g lipid/g glucose) was 0·14 and the fatty acids of lipids obtained were mainly oleic (C18:1), palmitic (C16:0) and stearic (C18:0).

Lipid production by an unsaturated fatty acid auxotroph of the oleaginous yeast Apiotrichum curvatum grown in single-stage continuous culture

An unsaturated fatty acid auxotroph of the oleaginous yeast Apiotrichum curvatum, named UfaM3, blocked in the conversion of stearic to oleic acid was cultivated in single-stage continuous culture. The influence of consumed carbon to nitrogen ratios (C/N ratios, g g−1) obtained at various dilution rates (D) on fatty acid (FA) accumulation and its profiles were studied. In continuous culture in N-limited medium a maximum FA accumulation of 45.6% (g g−1 of dry biomass) was obtained at an optimal D of 0.049 h−1, recording an efficiency of substrate conversion of 0.48 g g−1 and 0.22 g g−1 for biomass and lipids, respectively. The quality of lipid approached cocoa butter at an optimal C/N ratio of between 20 and 30. The C/N ratio in the incoming medium was 38.5 g g−1 with 30 g l−1 of glucose and both C and N sources were completely consumed at a critical D of ≤ 0.07 h−1. The stability of the mutant was demonstrated in the steady-state conditions of the chemostat with regard to the FA composition of its lipids.

Effect of various nutrient limitations on fatty acid production by Rhodotorula glutinis

The effects of nitrogen (N), phosphorus (P), zinc (Zn) or iron (Fe) limitations on lipid and especially α-linolenic acid (ALA) synthesis in the oleaginous yeast Rhodotorula glutinis have been investigated. Exhaustion of the limiting element in the medium resulted in an enhancement of both the fatty acid cell content (FA/X) and the corresponding productivity. Except for Fe-limited media, lipid accumulation was always coupled with an increase in the yield of ALA synthesis, whereas in all the limiting conditions the productivity of ALA declined. Kinetic investigations showed that this decline resulted from a sharp decrease in the specific rates of ALA synthesis associated with slowing down of growth. A comparative study showed that the highest yields and specific rates of fatty acid and ALA synthesis were induced by P-limitation early in the lipid accumulation phase. However, above a FA/X of 15%, N-limiting conditions become more attractive for producing lipids. During P-limited growth a down-shift of temperature from 30° C to 25° C was shown ao reduce the range of FA/X values at which the specific rate of fatty acid synthesis was maximal but without any other effect on fatty acid formation. In contrast, the decreased temperature resulted in enhanced ALA production by maintaining the specific rate of synthesis near to the maximal value of 3.6 mg gX−1h−1, where X* is free fatty acid biomass, and increased the corresponding yield by a factor of up to three.

Influence of pH, lactose and lactic acid on the growth of Streptococcus cremoris: a kinetic study

SummaryThe effect of various culture conditions on growth kinetics of an homofermentative strain of the lactic acid bacterium Streptococcus cremoris were investigated in batch cultures, in order to facilitate the production of this organism as a starter culture for the dairy industry. An optimal pH range of 6.3–6.9 was found and a lactose concentration of 37 g·l-1 was shown to be sufficient to cover the energetic demand for biomass formation, using the recommended medium. The study of the effect of lactic acid concentration on growth kinetics revealed that the end-product was not the sole factor affecting growth. The strain was characterized for its tolerance towards lactic acid and a critical concentration of 70 g·l-1 demonstrated. With the product yield of 0.9 g·g-1 at non-lactose limiting conditions the lactic acid concentration of 33 g·l-1 could not explain the low growth rates obtained, implicating a nutritional limitation.

Survival of alginate-entrapped cells of Azospirillum lipoferum during dehydration and storage in relation to water properties

Survival of alginate-entrapped cells of Azospirillum lipoferum was studied during dehydration using a dry air stream and during prolonged storage at various constant water activity values (aw). During the drying operation, the viability loss remained almost constant from the initial water content to 0.35 g water/g dry weight (DW) corresponding to a 98.5% water removal, strongly increased until a water content of 0.25 g/g DW and then stopped until the end of the drying operational (final aw 0.18). A water content of 0.25 g/g DW (aw=0.55) corresponded to the critical point of the moisture sorption isotherm curve from which water became restricted to the dry material. A high drying rate (5 g/g DW per hour) was shown to be more detrimental for cell viability than a low drying rate (1.18 g/g DW per hour). When the product was stored in a closed chamber with a regulated aw (0.23), the number of living cells decreased during a short period (less than 15 days) corresponding to the product aw stabilization, and then remained constant for more than 150 days. In addition, cell survival during storage was not affected by aw values in the range 0–0.55. Above aw=0.55, the higher the aw and the storage duration, the lower the residual survival percentage. The influence of the drying and storage conditions on the cell death rate are discussed with regard to both the mechanisms generally involved in viability loss and the hydration properties of water.

Kinetics of growth and fatty acid production of Rhodotorula glutinis

SummaryThe effect of culture conditions, especially nitrogen/carbon (N/C) ratio and temperature, on acyl lipid profiles in the oleaginous yeast Rhodotorula glutinis NRRL Y 1091 have been investigated. Cultivation of the microorganism under N-limited conditions (N/C < 0.14 g/g) resulted in enhanced fatty acid (FA) cell content but a reduced relative amount of polyunsaturated fatty acids (PUFA). The maximal FA productivity was obtained for a 0.025 N/C ratio resulting from the arrangement between the specific rate of FA synthesis and the concentration of lipid-free biomass. Under nitrogen-non-limiting conditions, cells grown at lower temperatures had a higher PUFA content and the maximal productivity of α-linolenic acid was obtained by shifting the temperature of the culture from 30° C to 25° C.

Effect of aeration rate and influence of pCO2 in large-scale cultures ofCatharanthus roseus cells

SummaryCatharanthus roseus cells were grown at various aeration rates using normal or CO2-enriched air. Kinetic data showed a detrimental effect of the increase of the gassing rate on the growth characteristics due to CO2 stripping. When the CO2 partial pressure in the culture was maintained at a constant level of 20 mbar, better growth and enhanced conversion yields were obtained.

Effect of carbon dioxide on the growth of cell suspensions ofCathakanthus roseus

SummaryGrowth parameters of Catharanthus roseus in suspension cultures were examined under various pCO2 conditions. In CO2-enriched environments (up to 2 %) for Erlenmeyer flask cultures, enhanced maximum growth rates and conversion yields were observed. Fermenter cultures with a constant pCO2 of 2 %, gave high conversion yields although no growth-promoting activity was observed. High aeration rates led to decreased rates of growth due to CO2 stripping.

Growth and lactic acid production by Lactobacillus casei ssp. rhamnosus in batch and membrane bioreactor : Influence of yeast extract and Tryptone enrichment

Enrichment of the medium with yeast extract (20 g.l ) and Tryptone (40 g.l ) increased the growth of Lactobacillus casei ssp. rhamnosusand its production of lactic acid in both batch and cell-recycle cultures without affecting glucose consumption and the lactic acid production rate.

Maintaining a controlled residual growth capacity increases the production of polyhydroxyalkanoate copolymers by Alcaligenes eutrophus

SummaryThe manner in which copolymer poly(HB-co-HV) production was influenced by different methods of limiting cell proliferation during the production phase was examined. Polymer production was significantly improved in fermentation strategies in which some growth was maintained, either by linear or exponential nitrogen source feeding as compared to cultures in which nitrogen supply was totally interrupted. Improved volumetric productivities were obtained in cultures fed with NH4OH and the proportion of 3HV incorporated was approximately twofold higher in these cultures. These performance improvements were due to higher specific rates of glucose and propionate consumption in cultures in which true growth capacity was maintained.